I’m trying to setup the full SSL option on my NGINX webserver. So:
– I’ve created my self-signed certificate and I’ve enable it through my configuration
– I know that I whitelisted permanently all the Cloudflare IPs ranges.
But it does not work. A strange issue appears: if I restart NGINX webserver and then I go to my website, the page loads as I expect. But then, if you reload it, the error 521 “Web server is down” is showed.
I’ve tried to investigate a little bit, and I did not find any debug, information and errors in NGINX logs. However, using tcpdump, I recognized one possible error. All the packets shows the checksum as failed. Then my server does not return anything.
linux_vps_.https > [REDACTED]: Flags [FP.], cksum 0x2163 (incorrect -> 0xed28), seq 19227:19258, ack 1283, win 252, options [nop,nop,TS val 2551152448 ecr 660729444], length 31